In microprocessors, such as the series of microprocessors sold by MOS Technology, Inc., of Pennsylvania under the designation 650X, as well as in other microprocessors and related memory devices, it is common to use so-called memory line driving circuits to raise the voltage level of a memory drive line, such as a row select line, depending on a certain combination of a control signal and two clocks. For example, the inputs to the driving circuit may be an operating voltage for the circuit, a control signal and a first clock and a second clock complementary to each other, and the circuit may be set up such that its output drive line is high when the control signal and the first clock are low but the second clock is high, while the same output drive line is low at all other times. It is common in such driving circuits to use an MOS transistor device operating in an enhancement mode as a couple between, on the one hand, the operating voltage source and the control signal source and, on the other hand, the second clock and the output line. The couple is used to minimize the capacitive coupling between the second clock and the side of the couple connected to the operating volage source and the control signal source, and to connect and disconnect one part of the driving circuit to or from another at appropriate times.
In accordance with this invention it has been discovered that while a couple of this type serves the function of coupling and decoupling the respective two sides of the circuit at the proper times, it also prevents the full voltage from the operating voltage supply and the clocks from appearing on the output driving line, and that a depletion rather than an enhancement couple may be used in a way which appears inappropriate for a depletion couple but in fact provides significantly improved results.
More specifically, it is believed that a certain combination of inherent device capacitances prevents a full voltage transfer to the output driving line in the conventional enhancement couple circuit, and that a depletion couple circuit, though seemingly inappropriate, in fact permits the full transfer of voltage to the output driving line, and additionally gives significant speed advantages over an enhancement couple. It is believed that the discovered workability of the depletion couple is at least in part due to a device body effect which has not been previously appreciated for depletion mode uses of this type.